Relative cross sections of the ${\rm B_c^+(2S)}$ and ${\rm B_c^{*+}(2S)}$ states with respect to the ${\rm B_c^+}$ state in proton-proton collisions at $\sqrt{s} = 13$ TeV

The ${\rm B_c^+(2S)}$ to ${\rm B_c^+}$ and ${\rm B_c^{*+}(2S)}$ to ${\rm B_c^+}$ cross section ratios, as well as the ${\rm B_c^{*+}(2S)}$ to ${\rm B_c^+(2S)}$ cross section ratio, are measured in proton-proton collisions at $\sqrt{s} = 13$ TeV, using a data sample collected by the CMS experiment, corresponding to an integrated luminosity of 143 fb$^{-1}$. The three measurements are made in the ${\rm B_c^+}$ phase space window defined by transverse momentum $p_{\rm T} > 15$ GeV and absolute rapidity $|y| < 2.4$, with the excited ${\rm B_c^{(*)+}(2S)}$ states reconstructed in their ${\rm B_c^+} \pi^+ \pi^-$ decay. The ${\rm B_c^+(2S)}$ to ${\rm B_c^+}$, ${\rm B_c^{*+}(2S)}$ to ${\rm B_c^+}$, and ${\rm B_c^{*+}(2S)}$ to ${\rm B_c^+(2S)}$ cross section ratios, including the (unknown) ${\rm B_c^{(*)+}(2S) \to B_c^+}\pi^+\pi^-$ branching fractions, are ${\rm (3.57 \pm 0.69~(stat) \pm 0.32~(syst))\,\%}$, ${\rm (4.91 \pm 0.69~(stat) \pm 0.57~(syst))\,\%}$, and ${\rm 1.39 \pm 0.35~(stat) \pm 0.09~(syst)}$, respectively, where the first uncertainty is statistical and the second is systematic. None of these ratios shows a significant dependence on the $p_{\rm T}$ or $|y|$ of the ${\rm B_c^+}$. The shape of the invariant mass distribution of the dipions emitted in the ${\rm B_c^{(*)+}(2S) \to B_c^+}\pi^+\pi^-$ decays is also reported.